Field of the Invention
The present invention relates to a printing apparatus and a print control method, and particularly to, for example, a printing apparatus that prints an image on a print medium using inkjet printheads and a print control method thereof.
Description of the Related Art
In recent years, an inkjet printing apparatus (to be referred to as a “printing apparatus” hereinafter) that prints an image by heating a plurality of print elements provided in each printhead to discharge ink droplets on a print medium such as printing paper or the like and causing the ink droplets to adhere to the print medium to form dots has become popular.
The driving operation of printheads that print by discharging ink has been performed in a conventional printing apparatus in the following manner.
FIG. 8 is a block diagram showing the arrangement of a printhead drive control circuit for driving printheads.
As shown in FIG. 8, a system clock (SCLK) is supplied to a heat pulse generator 71, a print data generator 73, and a block pulse generator 74. In addition, pulse setting information (to be described later) is supplied from a CPU (not shown) to the heat pulse generator 71 via a data bus and an address bus. Based on the control by the CPU, print data is supplied from a RAM 25 to the print data generator 73 and a start bit (START) instructing the start of printing is supplied to a latch pulse generator 75.
When the start bit is supplied, the latch pulse generator 75 supplies a latch pulse (LATCH) to a driving circuit of printheads 9. Furthermore, in synchronization with the system clock (SCLK), the heat pulse generator 71, the print data generator 73, and the block pulse generator 74 generate a heat pulse (HEAT), a print data signal (DATA), and a block pulse (BLOCK), respectively.
FIG. 9 is a timing chart of each signal of the printhead drive control circuit shown in FIG. 8.
The reciprocal of a period between two latch pulses (LATCH) is the print frequency, and ink is discharged from all the nozzles provided in the printhead 9 during this period. For example, 60 nozzles are divided into 6 ten-nozzle blocks in accordance with the block pulse (BLOCK) by a multiplexer provided in the printhead 9, and the nozzles belonging to each block are sequentially selected and driven.
Note that the pulse setting information is changed by the internal temperature of the printhead 9 and variations in heating characteristics of the heaters which are in the nozzles and used for ink discharge. This temperature information is transferred to the CPU via an A/D conversion circuit by a signal from a temperature sensor provided in the printhead. The CPU adjusts the value according to the transferred temperature information so that an appropriate heat pulse (HEAT) which is in accordance with the internal temperature of each printhead can be obtained.
However, according to the above-described conventional print head driving control, the timings of the leading edge and the trailing edge of the heat pulse are uncertain since each pulse width of the heat pulse (HEAT) changes depending on the internal temperature of the printhead.
In recent years, along with the increase in the number of nozzles provided in each printhead, the heat current that flows at the generation time of a heat pulse has increased and crosstalk occurring at the leading edge and the trailing edge of the heat current has become problematic. As shown in FIG. 9, crosstalk noise can be superimposed on the print data signal (DATA) at the timings of the leading edge and the trailing edge of the heat pulse (HEAT) in some cases.
A technique disclosed in Japanese Patent Laid-Open No. 2000-25228 considers the influence of crosstalk noise to a data clock (DCLK). More specifically, the technique adjusts the timings so that the leading edge and the trailing edge of the heat pulse (HEAT) will not overlap with the leading edge and the trailing edge of the data clock (DCLK) by delaying the data clock signal by one clock.
However, since the objective of the technique disclosed in Japanese Patent Laid-Open No. 2000-25228 is to prevent a case in which the print data signal (DATA) cannot be sampled at the point of change of the data clock (DCLK), it cannot prevent the influence of crosstalk noise on the print data signal (DATA) itself. Furthermore, since the data clock (DCLK) needs to be temporarily stopped, it is difficult to directly apply the technique proposed in Japanese Patent Laid-Open No. 2000-25228 to a case where data communication between the main body of the printing apparatus and the printheads is serial communication.
As an influence of crosstalk noise on the print data signal (DATA), there is the influence of waveform distortion in which the voltage amplitude temporarily changes. Particularly, in the case of LVDS (Low Voltage Differential Signaling) or the like, the distortion amount of the amplitude becomes large since the voltage amplitude is small, thereby increasing the possibility that a receiver may not be able to receive a signal normally. Typically, since LVDS uses a differential signal, LVDS has a high tolerability to common noise but has a low tolerability to differential noise.
In addition, to meet the recent demand for higher printing speed, the number of nozzles provided in each printhead is increasing. This increase in the number of nozzles leads to an increase in the total heat current necessary for ink discharge. The increase in the number of nozzles also requires an increase in the transfer speed of the print data signal that causes ink discharge from the nozzles. An increase in the heat current linearly increases the amount of crosstalk noise, and higher print data transfer speed increases the probability of receiving the influence of crosstalk noise.